1. Field of the Invention
This invention relates to the preparation of natural tissue for implantation, and more particularly, to the preparation for implantation of aortic heart valves having improved flow characteristics.
2. Description of Prior Art
Natural valves taken from animals, particularly porcine aortic valves, have been used for a number of years for replacement of diseased valves in humans. The valves are excised from the animal heart, fixed in an appropriate tanning fluid such as glutaraldehyde or formaldehyde, and mounted on a framework or stent for subsequent implantation. During the fixation procedure, it is necessary that coaption of the valve cusps be maintained in order to assure proper valve function after implantation. Originally, coaption was achieved by packing the valve with cotton, and more recently, by pressurizing the valve with the tanning solution. Pressure fixation is the preferred method and is described in detail in U.S. Pat. No. 4,050,893, incorporated herein by reference.
The right coronary cusp of a porcine aortic valve is identified by the presence of a muscle referred to as the septal shelf. The septal shelf forms part of the right coronary cusp leaflet and protrudes into the valve orifice, reducing the effective maximum orifice size of the valve. Fixation of the valve by either the cotton packing or pressure technique fixes the septal shelf in its natural position.
Valves having improved flow characteristics have been produced by surgically removing the right coronary valve cusp and septal shelf attached thereto, and replacing it with a similarly sized non-coronary cusp from another valve. The cusp replacement is done following fixation of the valve, and the resulting modified valve has a larger effective orifice and improved flow characteristics due to the absence of the septal shelf. Although this procedure is effective to produce an improved aortic valve, it significantly increases valve manufacturing costs in terms of labor, materials, lost productivity, and rejected goods.
It is accordingly an object of the present invention to provide a method for preparing an aortic valve for implantation which eliminates or substantially reduces the effect of the septal shelf. It is a further object of this invention to provide an aortic valve having improved flow characteristics relative to conventionally fixed valves. It is a further object of this invention to eliminate or reduce the effect of the septal shelf on valve performance without resorting to surgical modification of the valve. These and other objects of the invention will be apparent from the ensuing description and claims.